This invention relates to an ignition device adapted to be used for an internal combustion engine.
In the prior art field, there is an ignition device for an internal combustion engine in which a power switching part, a current limiting circuit acting as a protection function part, and a thermal shut-off circuit for forcing current flow to be blocked out at the time of abnormal heating are integrated on the monolithic silicon substrate of an IGBT, as shown in Japanese Patent Prepublication No. 335522/1986.
This prior art includes the current limiting circuit and thermal shut-off circuit acting as protection functions in an igniter, but since the thermal shut-off circuit has the function such that it detects abnormal current flow indirectly by monitoring the temperature of an element to force the gate signal of an IGBT to become low when the element temperature reached an established temperature, thereby to intercept the primary current flowing through an ignition coil, it is impossible to control the timing of generating electrical discharge at an ignition plug due to a high voltage at the secondary side of the ignition coil and there is a possibility that burning such as backfire, etc. occurs due to ignition during the intake stroke.
In order to resolve the above-mentioned problem of the prior art, this invention provides a latch control system having a timer for counting the on-time of an ignition controlling signal to detect directly the current flowing time thereby to force the primary current to be blocked in case where the ignition controlling signal of which duration is longer than a definite period of time is inputted and further to interrupt the current through the IGBT until this ignition controlling signal becomes low. Also, an electric potential comparison circuit is provided in the input stage, the operative voltage for the ignition controlling signal is used which has a threshold value and a hysterisis, and an NMOS transistor is formed within the self-separation layer in which these control circuits and the power IGBT part are isolated by a p-well layer.
As mentioned abode, with the latch control system having a timer for counting the on-time of an ignition controlling signal to detect directly the current flowing time thereby to force the primary current to be blocked in case where the ignition controlling signal of which duration is longer than a definite period of time is inputted and further to interrupt the current through the IGBT until this ignition controlling signal becomes low, it is possible to control the timing of the compelled blocking. Since the current flowing is not restarted during the abnormal current flowing condition once it is operated, it is possible to prevent the burning of the backfire, etc. Also, by providing the electric potential comparison circuit in the input stage and using the operative voltage for the ignition controlling signal having the threshold value and the hysterisis, it is possible to provide a large margin for external noises. Further, with the NMOS transistor formed within the self-separation layer in which the control circuits and power IBGT part are isolated by the p-well layer, it is possible to integrate them on the monolithic silicon substrate of the IGBT with the minimum number of processes, and to achieve a multifunctional one-chip igniter with high operative stability and reliability.